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(77-03) A fate and transport model to evaluate and manage agrochemical runoff and leaching from rice paddies. Cheplick, J. Mark*,1, Williams, W. Martin1, Capri, Ettore2, Zewai, Miao2, 1 897-B Harrison St, Leesburg, VA, USA2 Universita Cattolica del Sacro Cuore, Piacenza, Emilia-Romagna, Italia ABSTRACT- Existing pesticide transport models are not configured to simulate the flooding conditions, overflow, and controlled releases of water that are typical under rice production. A fate and transport model, RICEWQ, was developed to simulate water and chemical mass balance associated with these unique governing processes. Water balance accounts for precipitation, evaporation, seepage, irrigation, releases and overflow from various paddy outlet configurations, and controlled drainage prior to harvest. Chemical balance accommodates application, dilution, advection, volatilization partitioning between water/sediment, decay in water and sediment, burial in sediment, and resuspension from sediment. A second model, PRZM3/VADOFT was coupled to RICEWQ to provide the capability to assess leaching below the paddy. VADOFT is finite-element code for simulating moisture movement and solute transport in the vadose zone. The VADOFT code uses Richards' equation to simulate one-dimensional, single-phase moisture and solute transport in unconfined, variably saturated porous media. Transport processes include hydrodynamic dispersion, advection, linear equilibrium sorption, and first-order decay. The code predicts infiltration or recharge rate and solute mass flux entering the saturated zone. This paper describes in detail the model development, calibration procedures, and application in investigating the fate and transport to surface waters of agrochemicals used in rice production. Also described are application of the model in developing and evaluating the effectiveness of alternate agricultural best management practices (BMP's) for environmentally-sound chemical use. Key words: rice, ricewq, przm3/vadoft, runoff |
